1. Field of the Invention
The present invention relates to a projection system having increased optical efficiency by performing a color scrolling in the long axial direction of a light valve, and a color scrolling method therefor.
2. Description of the Related Art
Projection systems are classified into 3-panel projection systems and single-panel projection systems according to the number of light valves for controlling the on/off operation of light emitted from a high-output lamp on a pixel-by-pixel basis and forming a picture. The single-panel projection systems can have a smaller optical system than the three-panel projection systems but provide only ⅓ of the optical efficiency of the three-panel projection systems, because R, G, and B colors into which white light is separated are sequentially used. Hence, attempts to increase the optical efficiency of single-panel projection systems have been made.
In a general single-panel projection system, white light radiated from a white light source is separated into R, G, and B colors using color filters, and the three colors are sequentially sent to a light valve. The light valve operates according to the sequence of colors received and creates images. As described above, a single-panel optical system sequentially uses colors, so the light efficiency is reduced to ⅓ of the light efficiency of a three-panel optical system. A scrolling method has been proposed to solve this problem. In a conventional color scrolling method, white light is separated into R, G, and B color beams, and the three color beams are simultaneously sent to different locations on a light valve 100 as shown in FIG. 1. In other words, the light valve 100 is divided into three areas, and R, G, and B color beams are focused on their corresponding areas. Each of the color areas is referred to as a color bar. Since an image cannot be produced until the R, G, and B color beams respectively reach all pixels of the color areas in the light valve, color bars are moved at a constant speed by a color scrolling means. The movement of color bars is referred to as color scrolling.
In the above-described color scrolling method, three R, G, and B color beams are not sequentially used but simultaneously used. Accordingly, the optical efficiency of single-panel projection systems adopting the color scrolling method can be increased. In single-panel projection systems adopting this color scrolling method, the light valve 100 generally has a rectangular shape with an aspect ratio of 4:3 or 16:9. In the rectangular light valve 100, a shorter side is referred to as a short axial direction, and a longer side is referred to as a long axial direction. As shown in FIG. 1, R, G, and B color bars formed on the light valve 100 are shifted in the short axial direction of the light valve 100. The color bar shifting (i.e., color scrolling) in the short axial direction of a light valve is not good in view of optical efficiency. This will be compared with the present invention later.